1. Field of the Invention
The present invention is related to stator coil formers and, more particularly, to stator coil formers used in the manufacturing of large electric generators such as those used in power plants.
2. Description of the Related Art
Electric generators used to produce electricity in power plants have stator coils formed by two "half coils". Each half coil may be as long as 36 feet in a large generator and there may be around 60 in a small generator to as many as 120 in a large generator. The stator coils typically have a rectangular cross-section which may be up to 0.8 cm (2 inches) in width and up to 2.4 cm (6 inches) in height and are formed by stacking small insulated copper strands of multiple sizes, as illustrated in FIG. 3.
Conventionally, the insulated strands are stacked next to each other. Resin impregnated DACRON insulation is inserted between and around the stacks of insulated strands and all except the last four to six feet at each end is cured (the insulation is melted and solidified) while kept straight. Then, the ends of the half coil are formed in a complex curve so that the lead ends can be joined with another half coil to form a complete coil during assembly of the generator.
A stator coil former like former 20 illustrated in FIG. 1 is conventionally used to form the complex curved shape of the ends of half coils. The cured center portion 22 of a half coil is secured at the far side of the former 20 and the end 24 is bent from the straight position 24a indicated by dashed lines to the position indicated by solid lines to conform to forming surfaces 26, 28 and 30. This results in a formed stator coil end 24b like that illustrated in FIG. 2.
The conventional stator coil end former 20 illustrated in FIG. 1 is constructed in the following manner. The forming surface 26 is a portion of a cone having dimensions which are known from the size of the generator. The path taken by the stator coil across the cone is determined by the dimensions of the generator and the distance between the half coils which are joined to form a single coil. This shape is defined as an involute on the inside surface 26 of a cone. The involute shape is used so that the spacing between adjacent stator coil ends 24 arrayed on the conical surface is uniform and minimum electrical distances are maintained. Engineering drawings are produced indicating the shape of the half coil.
Using the engineering drawings, patternmakers produce patterns for forming a portion of the cone from laminated blocks of hardwood as illustrated in FIG. 1. The wood is conventionally carved by hand in a shape determined from the engineering drawings. Next, a recess is hand-carved out of the conical surface and a brass liner 32 is inserted to prevent the wood from being damaged. Then, wood patterns of shelves 34 and 36 having surfaces 28 and 30, respectively, are hand-carved to fit at an appropriate location on the conic surface 26. Conventionally there are three to four shelves 34 secured next to each other. Fantails (not shown) are carved into the ends of the wood patterns to fit the shelves 34 in the proper alignment. From these wooden patterns of shelves 34 and 36, aluminum castings are made which are ground, filed and hand fit to the conic surface 26 of former 20. Holes are drilled through the shelf sections 34 and 36 and the brass liner 32 which is then threaded so the shelves 34 and 36 can be bolted down. Holes (not shown) are then drilled in the shelves 34 and 36 so that clamps, heating elements and temperature controlling devices (not shown) can be inserted during the forming and curing of the coil ends. The coil end 24 is then manually formed by pounding, prying and wedging into position and clamped in place while heating elements are inserted into the previously drilled holes and insulation inserted between the insulated strands and wrapped around the strands, is cured. After the insulation solidifies, the stator coil end 24b maintains the shape in which it was secured during curing.
The stator coils are inserted around a generator as top and bottom half coils, each of which have geometrically different front and rear end turns. Therefore, a minimum of four stator coil formers are required for each generator, one for the top and bottom half coils at each end of the generator. Lower rated generators have equally spaced coils and require conventional coil formers 20 capable of producing stator coil ends 24 of only one shape. In higher rated generators, there can be as many as six groups of coils with each group separated by a greater distance than the distance between the coils within a group. Thus, each of the half coils within a group has a slightly different length and the coil former 20 is modified to handle these varying lengths. As a result, the cost and time required to produce coil formers is significantly increased for higher rated generators.